1. Field of the Invention
The present invention relates to a liquid crystal display and a backlight module thereof, and particularly to a high brightness liquid crystal display and a backlight module thereof.
2. The Related Art
Conventional backlight modules for use in rear projection displays such as liquid crystal displays are classified into two types, an edge-type and a direct type, depending upon the position of the light sources in the displays. Edge-type backlight modules are usually used in liquid crystal displays because they save space due to their thinness.
One conventional liquid crystal display has a structure as shown in FIG. 5. In this figure, the liquid crystal display 1 includes a backlight module 16 and a liquid crystal panel (not labeled). The liquid crystal panel is disposed on the backlight module 16.
The liquid crystal panel comprises a first and second substrates 10 and 14, and a liquid crystal layer 12 interposed between the pair of substrates 10 and 14. The first substrate 10 includes a first glass sheet 101 and a light polarizing film 102. The second substrate 14 includes a second glass sheet 141 and a light polarizing absorption film 142. The backlight module 16 comprises a light source 161, a light guide plate 162, a brightness enhancing film 163, a diffuser 164, and a reflector 165.
FIG. 6 is a partial essential optical paths view corresponding to FIG. 5. Light beams emitted from a light source 161 are converted to a planar light beam T by the backlight module 16, and then are projected into the light polarizing absorption film 142. The planar light beams T are randomly polarized into two linear polarized light beams, an s-polarization component and a p-polarization component (denoted by arrows s and p shown in FIG. 6). The polarization state of the s-polarization component is orthogonal to that of the p-polarization component. The light polarizing absorption film 142 has a polarization axis parallel to the s-polarization component, so the s-polarization component passes. The light polarizing absorption film 142 also has an absorption axis parallel to the p-polarization component, so the p-polarization component is absorbed. Therefore, only half of the light beams T can pass through the light polarizing absorption film 142. The light energy of the light beams T is not effectively used due to the light polarizing absorption film 142 absorbing half the light beams T, and the brightness of the liquid crystal display 1 is low.
To solve the above problems, a liquid crystal display 2 shown in FIG. 7 is described in U.S. Pat. No. 6,448,955. The liquid crystal display 2 comprises a liquid crystal panel (not labeled) and a backlight module 26. The liquid crystal panel is disposed on the backlight module 26.
The liquid crystal panel is similar to that shown in FIG. 5 and includes a first and second substrates 20 and 24, and a liquid crystal layer 22 interposed between the pair of substrates 20 and 24. The backlight module 26 consists of two light sources 2611, 2612, two light guide plates 2621, 2622, a brightness enhancing film 263, a diffuser 264, a reflector 265, and a reflective polarizing element 266. The light sources 2611 and 2612 are disposed adjacent to the light guide plates 2621, 2622, respectively. The reflector 265, the light guide plates 2622, 2621, the diffuser 264, the brightness enhancing film 263, and the reflective polarizing element 266 are stacked together in order.
FIG. 8 is a partial essential light paths view corresponding to FIG. 7. Light beams T are randomly polarized, and consist of two linearly polarized light beams, an s-polarization component and a p-polarization component (denoted by arrows s and p shown in FIG. 8). A polarization state of the s-polarization component is orthogonal to that of the p-polarization component. The reflective polarizing element 266 has a polarization axis parallel to the s-polarization component, so the s-polarization component can pass. The reflective polarizing element 266 also has a reflection axis parallel to the p-polarization component, so the p-polarization component is reflected to the reflector 265. The reflected p-polarization component is partially converted to an s-polarization component, which then passes through the reflective polarizing element 266. The structure described above can reuse the reflected p-polarization component, and increases an amount of the light energy produced by the liquid crystal display 2.
Although the liquid crystal display 2 can reuse the reflected p-polarization component, the efficiency is poor due to a plurality of interfaces through which the reused reflected p-polarization component must pass. Furthermore, the liquid crystal display 2 needs an additional reflective polarizing element, so the manufacturing cost is high.
An improved liquid crystal display that overcomes the above-mentioned disadvantages is desired.